1. Field of the Invention
The present invention relates to compounds and compositions and methods of use thereof, useful for treating viral infections, in particular human papillomavirus.
2. Background
Human papillomavirus (HPV) is one of the most prevalent sexually transmitted infections in the world. There are more than 100 different types of HPV, the majority of which are harmless. However, there are about 30 types that are spread through sexual contact. Some types of HPV cause genital warts, which appear as single or multiple bumps in the genital areas of men and women including the vagina, cervix, vulva (area outside of the vagina), penis, and rectum. Although many people infected with HPV have no symptoms.
While most HPV subtypes result in benign lesions, certain subtypes can lead to more serious lesions. Anogenital infections arising from HPV-16 and HPV-18, while less common than HPV-6 and HPV-11, are most often associated with precancerous lesions in cervical and anal tissues called dysplasias. Patients with dysplasias are often asymptomatic and may only discover their lesion after screening. High-grade dysplasias, if left untreated, may transform into cancerous tissues. Low-grade lesions may spontaneously regress, while others may progress to high-grade lesions. HPV-16 and HPV-18 are most often associated with dysplasias, though several other transforming HPV subtypes are also associated with dysplasias. Recent studies indicate that up to 89% of HIV positive homosexual males may be infected with these high-risk subtypes of HPV. HIV positive patients are also more likely to be infected with multiple subtypes of HPV at the same time, which is associated with a higher risk of dysplasia progression.
Genital warts are the most common sexually transmitted disease in the world and are most prevalent in people 17-33 years of age. HPV-6 and HPV-11 are responsible for nearly 90% of all genital warts, but are rarely associated with neoplastic growths. According to the American Social Health Association, at least 20 million people in the US are currently infected with HPV, with 5.5 million new cases of sexually transmitted HPV infections occurring annually. Genital warts usually produce painless-itchy bumps located on or near the genitalia, but without treatment, may progress to larger more pronounced cauliflower-like growths. Roughly two-thirds of people who have sexual contact with a person infected with genital warts will develop warts within three months of contact. Spontaneous regression of genital warts occurs in 10-20% of genital wart cases. However, even if a lesion regresses, recurrence of genital warts is common with 50% recurrence after one year. As a result of the unsightly lesions, treatment of genital warts is common.
Evidence over the last two decades has led to a broad acceptance that HPV infection is necessary, though not sufficient, for the development of cervical cancer. The presence of HPV in cervical cancer is estimated at 99.7%. Anal cancer is thought to have a similar association between HPV infection and the development of anal dysplasia and anal cancer as is the case with cervical cancer. In one study of HIV negative patients with anal cancer, HPV infection was found in 88% of anal cancers. In the U.S. in 2003, 12,200 new cases of cervical cancer and 4,100 cervical-cancer deaths are predicted along with 4,000 new cases of anal cancer and 500 anal-cancer deaths. While the incidence of cervical cancer has decreased in the last four decades due to widespread screening, the incidence of anal cancer is increasing. The increase in anal cancer incidence may be attributed in part to HIV infection since HIV positive patients have a higher incidence of anal cancer than the general population. While anal cancer has an incidence of 0.9 cases per 100,000 in the general population, anal cancer has an incidence of 35 cases per 100,000 in the homosexual male population and 70-100 cases per 100,000 in the HIV positive homosexual male population. In fact, due to the high prevalence of anal dysplasia among HIV-infected patients and a growing trend of anal cancers, the 2003 USPHA/IDSA Guidelines for the Treatment of Opportunistic Infections in HIV Positive Patients will include treatment guidelines for patients diagnosed with anal dysplasia.
There is no known cure for HPV. There are treatments for genital warts, though they often disappear even without treatment. The method of treatment depends on factors such as the size and location of the genital warts. Among the treatments used are, Imiquimod cream, 20 percent podophyllin antimitotic solution, 0.5 percent podofilox solution, 5 percent 5-fluorouracil cream, and Trichloroacetic acid. The use of podophyllin or podofilox is not recommended for pregnant women because they are absorbed by the skin and may cause birth defects. The use of 5-fluorouracil cream is also not recommended for pregnant women. Small genital warts can be physically removed by freezing (cryosurgery), burning (electrocautery) or laser treatment. Large warts that do not responded to other treatment may have to be removed by surgery. Genital warts have been known to return following physical removal, in these instances α-interferon have been used to directly inject into these warts. However, α-interferon is expensive, and its use does not reduce the rate of return of the genital warts.
As such there exists an unmet need for effective HPV treatment. It has now been surprisingly discovered compounds that meet this need, and provide other benefits as well.